1. Field of the Invention
The present invention relates to a transmitting system utilized in a small-sized vehicle such as a two-wheeled motor vehicle and a four-wheel buggy, and particularly, to an improvement in a transmitting system, in which a crankshaft of an engine and an input shaft of a multi-stage transmission disposed in parallel to the crankshaft are connected to each other through a fluid transmitting means including a pump impeller connected to the engine, and a turbine impeller connected to the multi-stage transmission.
2. Description of the Related Art
There is such a conventionally known transmitting system for a small-sized vehicle, in which a fluid transmitting means is comprised of a torque converter, as disclosed in Japanese Patent Application Laid-open No. 57-69163.
In the transmitting system described in the above Japanese Patent Application, the crankshaft of the engine and the input shaft of the multi-stage transmission are connected to each other only through the torque converter, so that a torque shock generated at the start of the vehicle or during the shifting is absorbed by a slipping effect of the torque converter.
However, the torque converter and a fluid coupling have a slipping function, but as long as power is input from the engine, the transmission of a torque is conducted more or less. Therefore, the known transmitting system suffers from the following problem. At the start of the vehicle at which a transmission is switched over from a neutral position to a low position, such a creep phenomenon occurs that power is transmitted to some degree to a driving wheel of the vehicle, even if the engine is in an idling state. Another problem is that during traveling of the vehicle, a friction due to the transmitted torque always occurs at switchover sliding portions of the transmission and hence, the switchover resistance of the transmission is large, and a large shifting load is required. In addition, the torque converter is mounted to the input shaft of the multi-stage transmission driven in a reduced manner from the engine and for this reason, the transmitted torque borne by the torque converter is relatively large and hence, the large-sized torque converter having a large capacity is obliged to be used, which makes it difficult to make compact a power unit including the engine and the transmission.
Accordingly, it is an object of the present invention to provide a transmitting system of the above-described type for a small-sized vehicle, in which the creep phenomenon is eliminated, and the shifting operation of the transmission can be conducted lightly and moreover, which is of a simple construction and has a good assemblability.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a transmitting system for a small-sized vehicle in which a crankshaft of an engine and an input shaft of a multi-stage transmission disposed in parallel to the crankshaft are connected to each other through a fluid transmitting means including a pump impeller connected to the engine, and a turbine impeller connected to the multi-stage transmission, wherein a first reducing device, the fluid transmitting means and a shifting clutch which are disposed on the crankshaft of the engine sequentially in the mentioned order from one side wall of a crankcase supporting the crankshaft with a bearing interposed therebetween toward the outside, the shifting clutch having an input member connected to the crankshaft and an output member connected to the pump impeller, the turbine impeller being connected to a driving gear of the primary reducing device, a driven gear of the primary reducing device being connected to the input shaft of the transmission, wherein the axial movements of the input member, the pump impeller and the turbine impeller on the crankshaft are restrained by the bearing and a nut threadedly fitted at a tip end of the crankshaft.
With the first feature, during idling of the engine, the transmission of power to the shifting clutch and the like can be cut off, even when the transmission is in a low position, irrespectively of the presence of the fluid transmitting means, by controlling the shifting clutch to its turned-off state, thereby preventing a creep phenomenon. During a shifting operation, the transmission can be brought into an unloaded state, irrespective of the presence of the fluid transmitting means, by first controlling the shifting clutch to its turned-off state, whereby the shifting operation can be conducted lightly without being attended with a torque shock.
Moreover, the crankshaft is rotated at a high speed from the input shaft of the transmission driven through the reducing device by the crankshaft and hence, the transmitted torque borne by the fluid transmitting means and the shifting clutch mounted to the crankshaft is relatively small. Therefore, the capacities of the fluid transmitting means and the shifting clutch can be correspondingly reduced, leading to the compactness of the fluid transmitting means and the shifting clutch, and the power unit can be constructed compact, despite the provision of both the fluid transmitting means and the shifting clutch.
In addition, the primary reducing device is disposed at a location nearest to a sidewall of the crankcase and hence, a bending moment applied to the crankshaft and the input shaft of the transmission with the operation of the primary reducing device can be minimized. The fluid transmitting means has a weight larger than that of the shifting clutch, but is disposed at a location nearer to the sidewall of the crankcase than the shifting clutch. Therefore, the bending moment applied to the crankshaft can be minimized by the weights of the fluid transmitting means and the shifting clutch. As a result, it is possible to contribute to an enhancement in durability of the crankshaft, the input shaft of the transmission and the bearing supporting them in cooperation with the compactness of the fluid transmitting means and the shifting clutch.
Further, the input member, the pump impeller, the turbine impeller and the driving gear can be mounted to the crankshaft by the single nut, thereby simultaneously providing the simplification of the construction and an enhancement in assemblability.
Moreover, a thrust load generated between the pump impeller and the turbine impeller is borne by the crankshaft through the bearing and the nut and hence, it is possible to alleviate the load to be borne on the crankcase to contribute to an enhancement in durability of the crankcase.
According to a second aspect and feature of the present invention, in addition to the first feature, the crankshaft includes a large-diameter shaft portion located adjacent to the bearing, a small-diameter shaft portion connected to a tip end of the large-diameter shaft portion through a step, and wherein the input member is clamped and fixed on the small-diameter shaft portion by the step and the nut threadedly fitted at a tip end of the small-diameter shaft portion, and the axial movements of the pump impeller and the turbine impeller are restrained by the bearing and the input member.
With the second feature, the input member can be firmly fixed to the crankshaft by the step on the crankshaft and the nut. Moreover, the input member and the bearing restrain the axial movements of the pump impeller and the turbine impeller. Therefore, exclusive retaining members for these impellers are not required, leading to a simplified construction.
According to a third aspect and feature of the present invention, there is provided a transmitting system for a small-sized vehicle in which a crankshaft of an engine and an input shaft of a multi-stage transmission are connected to each other through a fluid transmitting means including a pump impeller connected to the crankshaft, and a turbine impeller connected to the input shaft, wherein a shifting clutch is interposed between the crankshaft and the input member in a series relation to the fluid transmitting means, the fluid transmitting means and the shifting clutch being disposed coaxially, so that a portion of an outer surface of the bowl-shaped pump impeller of the fluid transmitting means is received in a recess existing in one side of the shifting clutch.
The fluid transmitting means corresponds to a torque converter in each of embodiments of the present invention, which will be described hereinafter.
With the third feature, during idling of the engine, the transmission of power to the shifting clutch and the like, even when the transmission is in a low position, can be cut off, irrespectively of the presence of the fluid transmitting means, by controlling the shifting clutch to its turned-off state, thereby preventing a creep phenomenon. During a shifting operation, the transmission can be brought into an unloaded state, irrespective of the presence of the fluid transmitting means, by first controlling the shifting clutch to its turned-off state, whereby the shifting operation can be conducted lightly without being attended with a torque shock.
Moreover, when the fluid transmitting means and the shifting clutch are disposed coaxially, a portion of the outer surface of the bowl-shaped pump impeller of the fluid transmitting means is received in the recess existing in one side of the shifting clutch. Therefore, the recess in one side of the shifting clutch, i.e., a dead space, can be utilized effectively for the disposition of the pump impeller, leading to the compactness of the entire transmitting system.
According to a fourth aspect and feature of the present invention, in addition to the third feature, the recess is an opening in a bottomed cylindrical clutch casing of the shifting clutch.
With the fourth feature, a relatively large dead space present in the opening in the clutch casing can be utilized effectively for the disposition of the pump impeller, thereby effectively providing the compactness of the entire transmitting system.
According to a fifth aspect and feature of the present invention, in addition to the fourth feature, the pump impeller and the shifting clutch are connected to each other within the opening.
With the fifth feature, the opening can be utilized for the disposition of connected portions of the pump impeller and the shifting clutch, thereby providing not only the compactness of the entire transmitting system, but also an enhancement in connecting assemblability of the pump impeller and the shifting clutch.
The fluid transmitting means corresponds to each of torque converters T, Txe2x80x2 in first and second embodiments of the present invention, which will be described hereinafter; the input member of the shifting clutch corresponds to a clutch casing 27 in the first embodiment and a driving plate 81 in the second embodiment; and the output member of the shifting clutch corresponds to a friction clutch plate 23 in the first embodiment and an output member 84 in the second embodiment.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.